sedimentary

Chert (Flint/Jasper)

Microcrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale; Color: typically dark gray, black, or brown with iron staining; Luster: waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: none (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 on Mohs scale
Color: typically dark gray, black, or brown with iron staining
Luster: waxy to dull

Identified June 21, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed in marine environments through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or through the chemical precipitation of silica in groundwater. Often found as nodules in limestone or chalk beds.

Uses & applications

Historically used for stone tools and weapons (arrowheads); currently used in road construction, as an abrasive, and sometimes as a low-cost gemstone for lapidary work.

Geological facts

Flint is a variety of chert that was essential to human survival for millennia due to its ability to create sparks when struck against steel and its razor-sharp edges when broken.

Field identification & locations

Identified in the field by its waxy appearance, extreme hardness (scratches glass), and distinctive shell-like (conchoidal) fracture patterns. Commonly found in riverbeds or coastal chalk cliffs.

Other sedimentary specimens

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Sandstone or Siltstone

Arenite (if sandstone)

Sedimentary

Cone-in-cone structure (Limestone)

Cone-in-cone structure (Secondary Sedimentary Structure)

sedimentary

Chert Breccia

Brecciated Chert (Microcrystalline Silica)

sedimentary

Sandstone Grain

Clastic Sedimentary Rock Grain (SiO2 dominated)

sedimentary

Shale or Slaty Mudstone

Argillaceous sedimentary rock

sedimentary

Sandstone

Arenite (primarily SiO2)

sedimentary